Criticism Mounts of the Hyperloop

In recent days several writers and analysts have taken a closer look at Elon Musk’s proposed Hyperloop and found serious flaws in the proposal. One of these critics is Matt Johnson of Greater Greater Washington who argues the math doesn’t add up:

The Hyperloop pods will travel at up to 760 miles per hour, just under the speed of sound, with pods traveling about 30 seconds apart in the tube. They will have a maximum deceleration of 0.5 gs, which is equivalent to 10.9 mph per second. At that rate of braking, it will take a pod 68.4 seconds to come to a full stop.

That’s a pretty significant issue because safe vehicle operation means never getting closer to the vehicle ahead than the distance it will take you to stop. If pod A were to experience a catastrophic air-skid failure, crash into the tube wall, and disintegrate, pod B, 30 seconds back, would not be able to stop short of the wreckage. In fact, pod C would also likely hit the wreckage of pods A and B.

That means that the minimum separation between pods is probably closer to 80 seconds or more. Not a big deal. It still means 45 departures per hour. But that’s only 1,260 passengers per hour in capacity. That’s 10% of what the California High-Speed Rail can carry.

With a capacity of 1,260 passengers per tube, that means that the Hyperloop would need 10 tubes in each direction (not 1) to move the same number of passengers as the proposed high-speed line. And that would push the cost up by 10, which is actually more than the cost of the HSR.

Johnson also points out the Hyperloop proposal isn’t from downtown San Francisco to downtown Los Angeles – it’s from Oakland to Sylmar. That won’t serve the same market as HSR intends to serve, and while HSR plans to share tracks from Sylmar to Union Station, Musk has no provision for service to downtown LA.

Johnson also provides a good analysis of the idea of using an elevated guideway for the Hyperloop, pointing out the significant engineering challenges this would entail and the high costs that come with it. His analysis concludes that it’s very hard to see how the Hyperloop could be built for the absurdly low $6 billion cost that Musk proposes.

Alon Levy takes a look at the physics of the Hyperloop and concludes it’s a barf ride:

This is worse than sideways acceleration: track standards for vertical acceleration are tighter than for horizontal acceleration, about 0.5-0.67 m/s^2, one tenth to one seventh what Musk wants to subject his passengers to. It’s not transportation; it’s a barf ride.

Levy takes a look at the estimates for Hyperloop energy consumption and comes to a damning conclusion:

Indeed, a train with a thousand seats, 20 MW of power drawn, 60% seat occupancy, and a speed of 360 km/h can only ever expend 333 kJ per passenger-km while accelerating, and much less while cruising (acceleration at lower speed requires more energy per unit of distance, but cruising at lower speed expends only a fraction of the energy of full-power acceleration). Tesla’s train energy consumption numbers do not pass a sanity check, which suggests either reckless disregard for the research or fraud. I wouldn’t put either past Musk: the lack of references is consistent with the former, and the fact that Musk’s current primary endeavor is a car company is consistent with the latter.

And even the comedians are getting in on the act, with The Daily Show’s John Oliver mocking the Hyperloop:

Yet the tech geeks remain excited by the Hyperloop – because they can’t come to accept that high speed rail is itself a big leap forward, a cutting edge yet proven technology that moves a lot of people at speeds no land-based technology has yet been able to provide on a regular basis. Here’s Gizmodo making the case against bullet trains:

And yet the proposed high-speed rail line in California isn’t a big enough step forward by many accounts. It’s not using the fancy magnetic levitation technology being implemented in places like Japan and Germany, which will allow trains to fly down the tracks at over 300 mph. The trip from San Francisco to Los Angeles would take 2 hours and 38 minutes, an average speed of 164 miles-per-hour, which is pretty zippy compared to what we’ve had in the United States before, but not all that impressive by global standards. And as Musk points out, it’s not even really energy-efficient, when you consider the per-passenger energy expenditure.

Except the “fancy magnetic levitation technology” isn’t being implemented on a broad scale anywhere, including Japan and Germany. Maglev has never gotten beyond use on a few small short routes, in part because it is a huge technological leap forward that comes at an enormous cost. High speed trains that can break 200 mph are cutting edge and represent the innovative frontier of land-based transportation. Musk has done a good job convincing the media that he is the next step forward and trains are passé, but the vactrain that is the basis of Musk’s idea is itself a century old.

Much of the media coverage of the Hyperloop follows Musk’s own framing, which is basically that high speed rail sucks and that we should build something like the Hyperloop despite the fact that HSR is a proven technology and the Hyperloop isn’t.

There’s no good reason to pit these against each other. California HSR serves a hundred million more riders than the Hyperloop would, for a predictable cost with off-the-shelf technology. It’s about to begin construction and will do a huge amount of good for the state’s economy, energy independence, and carbon reduction efforts. The Hyperloop is also an idea worth exploring and perfecting. But it isn’t an alternative to or a replacement for high speed rail, and it should certainly not be treated as such.

Yet that is how the Hyperloop has been sold by Musk and reported by the media. That reveals not a fetish for new technology, but an anti-rail bias that is hard to understand or defend. As Amtrak’s record ridership shows, Americans and Californians in particular really like passenger trains and want more of them. Electrified trains reduce carbon emissions and provide a lot of people with a reliable, affordable, fast way to get where they want to go. Build more trains, of all kinds, should be a top national priority. I can dream that someday I will ride the Hyperloop between SF and LA. But I know for a fact that within the next 20 years I absolutely will ride the bullet train between SF and LA. That knowledge makes all the difference.

Y’all are missing the point by dumping on Musk. His ideas are very much akin to Bechtel’s BART vactrain that Bechtel promised the voters in 1962. So it is ok for Bechtel to bullshit but not an inventor?

You are making a big mistake in your dismissal of Musk – he is exactly the kind of person you need to support your CAHSR scheme. Who do you think the handful of serious transport investor types, like Branson, are going to listen to: a bright bulb like Musk or a dimbulb like Richards? If they even get so far as to allocate the money to perform an analysis they will come up with same conclusion as Musk, SNCF, and Van Ark. Even Kopp is pretty much of that opinion now.

John Bacon Reply:August 16th, 2013 at 3:00 pm

A 7’4” diameter one inch thick steel tube would have 10.5 times the volume, weight, and cost of steel per unit length as a pair of 135 Lbs. per yard rails: (62.4*7.87/(12^3))*(88*∏*36)/(2*135) = 10.48.
An evacuated tube would have less air-friction at the cost of higher initial cost and lower efficiency linear induction motor traction system. My experience as a motor and switching power design engineer indicates allowing only short magnetic circuit air gaps between a motor’s armature and stator, or their linear induction motor (LIM) equivalents, is important in order to create an efficient motor. Sustaining a LIM to guide-way gap tolerance anywhere close to the armature-stator bearing-frame structure gap control attainable in conventional motor designs appears wildly optimistic.
Consider the following balancing speed data for a Shinkansen Series 300 (operating between 1992 and 2012) conventional hsr train: 12,000 kw*hr, 296 km/hr, 1323 seats. Power cost = (12,000*$0.11)/(296*1323) = $0.00337 per passenger-seat-kilometer = $0.00542 per passenger-seat-mile. Use the railway traction power consumption equation: P = V*(R + W*(V^2)*M*G but drop the rolling friction plus climbing rate factor ‘R’ (negligible for the next level-ground power consumption per unit distance traveled estimate). In order to be responsive to the universal truth that as speed rises distance traveled rises by the same speed factor dropping one ‘V’ factor makes sense. Within the high speed range being considered the simplified equation P ≈ W*(V^2)*M*G will be less than 1% in error due to deleting the R = 0.001 factor. Raising speed to 220 mph (354 kph) and assuming a later model hsr train will have a 20% lower wind resistance constant the power cost will rise to $0.00542*0.8*(354/296)^2 = $0.00621 per passenger-seat-mile. Raising speed to 400 kph and using the same 296 kph base-line the cost per passenger seat mile would rise to: $0.00542*0.8*(400/296)^2 = $0.00792. Even if you ran the LA to SF road distance at 400 km/hour the power cost would be $3.08 per seat. For a realistic speed profile total power consumption would be considerably lower than $3.00 per seat for an LA to SF trip.

Nathanael Reply:August 17th, 2013 at 1:07 am

Musk’s “hyperloop” proposal is idiotic, commercially speaking. He should have actually looked up civil engineering costs before he started, because his pricing is off by a factor of 10.

To his credit, he clearly knows somewhere in his head that the proposal is idiotic, because he hasn’t started a company to build it.

This is in contrast to the business models of SpaceX (replace expensive electromechanical components in rocketry with electronics) and Tesla (sell electric cars to the rich to pay off capital and R&D costs of setting up a new car company), both of which actually make sense.

Thermal expansion of steel is 13 (10-6 m/m K) and temperatures in Fresno vary from 3C to 37C, so a 640km long steel pipe would be 282m longer in Summer than in Winter.
No problem, just assemble the pipe and fix it firmly in place in the height of summer, in the winter the steel will stretch to fit.

aw Reply:August 16th, 2013 at 12:18 pm

The obvious solution is to include expansion joints in the tubes, just like is done with bridges. How you would design such an expansion joint that didn’t leak would be the next problem.

thatbruce Reply:August 16th, 2013 at 12:58 pm

@aw:

A telescoping tube, similar to the boxy ones used to access airplanes at airports would be needed at the end stations to address the cumulative length change of the tube.

Obviously these ‘telescoping tubes’ would need to be more frequent in areas of frequent thermal changes.

Hyperloop is like the late 1990s Maglev proposal–starve existing transportation while chasing the end of the rainbow. Where is that Maglev now, I wonder? I guess somebody in Washington took some sanity pills and killed it. They were going to test it Washington to Baltimore when the real problem on that segment is a 30mph urban tunnel that nobody wants to cough up the money to replace. I guess fixing what’s broken is less exciting than whizbang projects that will never see completion.

Whizbang projects that will never see completion, that’s the whole point of Repubs/baggers, HSR was supported by Repubs/baggers so long as it never became real(Like under Gov Arnold Schwarzenegger, He did really want HSR & I believe He still does), once it becomes real it’s a threat to Big Oil, a very major Repub/bagger campaign contributor, so naturally Repubs/baggers in Government are now against HSR anywhere in the USA, CA HSR is one that they desperately want to squash at all costs… FLAT…

The capacity issue was one of the first things i noticed. The whitepaper mentions around 800 passengers per hour. HSR is being designed to 39,000 passengers per hour. Im not sure how HL can be considered comparable to HSR. Also, what of the issue of safety, specifically a fire? How do first responders get to a pod on fire given that it would be contained in an 8ft seamless steel tube? Will local fire departments along the length of the tube be equipped and trained to do this safely? Also, what happens when you ‘break the vacuumed seal’? Would the equivalent of 700 miles of tube air volume rush in instantly, fanning the flames and further torching the passengers?

The speed of sound in a gas is approximately constant versus pressure (the speed of sound in the low pressure Hypertube is about 760 mph). But, the speed of sound is inversely proportional to the square root of the molecular weight of the gas. So, to increase the speed of sound in the tube by a factor of three, use helium inside it instead of air.

nobody_important Reply:August 16th, 2013 at 11:07 am

Helium is in short supply these days. In fact, it will run out unless we can get more from the moon.

tbert Reply:August 18th, 2013 at 1:49 pm

Holy balls, every time I hear some dumbass talk about mining helium “from the MOOOONNN!!!” I want to box them on rhe ears and shout “fuse the hydrogen in seawater, Einstein”. Guarantee that’s a solution that lives in this world, and not just fevered techo-fantasies. Get a grip on science, people.

agb5 Reply:August 16th, 2013 at 11:18 am

There is not enough Helium in the world to fill a pipe 2m in diameter by 640km long.
Helium, being a small molecule constantly leaks through the walls of any container so you would constantly have to buy more.
When CERN was designing the Lare Hadron Collider, there was initially a concern that it would take the world’s entire output of Helium to run the cryogenics.

Very much off topic, but does anyone know where the ridership data from San Francisco’s Transit Effectiveness Project went? It used to be located here, but that link is now dead and the SFMTA insists on excluding itself from the Wayback Machine. This page listed the ridership of each MUNI line, as well as some accompanying maps of station usage.

Because a differential would cause even more wear on straight lines. It is just the fact that the wheelsets are one part, together with the conical running surface of the wheels that the vehicle is stable.

There are vehicles which do not squeal around tight curves (for example the Cobra in Zürich), which have “electric differentials”, but their wheel wear is horrendous, and there are good reasons why they got the nickname “rattlesnake”…

Jonathan Reply:August 16th, 2013 at 5:30 pm

the wheels are rigidly mounted on solid axles. Bogies, or trucks, are rigid frames which hold a pair of axles. The body of the BART cars is mated to one bogie, close to each end. (I’m ignoring driven axles, but the axles are just that, *driven* solid axles).

Unlike a typical car or truck, there’s no hollow axle and no inner axle-shaft supported by bearings, and engaging a differential in the middle of the axle housing.

The closest I can think of to a differential, is used in model garden railways, where long cars run through obscenely tight curves. In that scenario, some people use ball-bearing wheels, with a sealed ball-bearing pressed onto the end of the axle. The wheel/flange is bored to about 2x the diameter of a normal wheel, and pressed onto the outer surface of the ball-bearing.

Rail vehicles are designed to use wheels with coned tread and flanges. Even “normal” trains can generate wheel-squeak going through tight curves.

Nathanael Reply:August 17th, 2013 at 1:04 am

Certain Talgo designs have independently mounted left and right axles, which eliminates a lot of the wheel squeal.

No differential needed, obviously.

(For those who don’t see why it’s obvious, in a modern electric train, each driven axle *has its own motor*. You can do any differential stuff in software.)

A funding plan put forth by the California High-Speed Rail Authority in 2011 violated several provisions of Proposition 1A, a $9.9 billion bond measure, according to a ruling issued late Friday by a Sacramento Superior Court judge.

In the lawsuit by Kings County, Hanford resident Aaron Fukuda and Kings County farmer John Tos, the ruling by Judge Michael Kenny pointedly notes that “the Authority abused its discretion by approving a funding plan that did not comply with the requirements of the law.”

But Kenny’s ruling also asks for more arguments from both sides before he determines whether to issue a court order to overturn the rail agency’s approval of its business plan or to negate the state Legislature’s approval last summer of about $2.6 million from Prop. 1A for construction to begin.

I’m going to try posting something about construction costs of non-conventional rail. I have numbers for some elevated monorail projects (and Hyperloop’s idea of a slick, thin structure evokes monorail, as do the weight-based defenses of the cost estimates), and I’m going to try getting more, and maybe also numbers for elevated low-speed maglev.

Curious to listen to response from Musk and his engineers. So lets say they increase the size of the pods to 3 times and then stick to 90 seconds gap. Then we have a train which can a lot of passengers at one time. Key here is “One time”. I do not have a choice to leave at whatever time I want. People travelling from LA and SF will mostly not stick to the standard office times. Over the long week ends heck there will be people who will leave all the way from evening to morning… Did we consider how many. Can we have a high speed railway every 45 minutes (the approximate calculation to carry the same number of passengers). These Pods do not need to run empty. They can just not run when not required. Can we do that with high speed railway except reducing the length of the train? How much effort does it take?

Hyperloop is not as heavy as train. So the construction is not going to require elevated platform to carry huge loads.

I say, lets Musk build a prototype and I will be more than happy to work for free few hours a week for this purpose. If it fails it fails! big deal we tried. Dismissing out rite is foolish.